Quillgin is the main antagonist of the Regular Show episode "The Christmas Special". He was a former scientist at Santa Claus' Toy Factory who later betrayed him and tried to destroy Christmas.
As the lead toy designer of Santa Claus, he spent his life working on a present that will give children anything they were anticipated for. He used dark magic as a key component. In testing the box, people turned evil, so Santa ordered his elves to destroy Quillgin's life's work, leading to Quillgin's breakout.
During the night of the Christmas Day, Quillgin assaulted the Toy Hangar and stole his creation in order to destroy Christmas forever and also stole Santa's Sled as a mode of transport. However, Santa appeared in scene and was apparently killed by Quillgin and took the present with him during the fall much to Quillgin's dismay.
After he discovered that Mordecai, Rigby and the other employees of the Park had his present, Quillgin and his elves allies infiltrated into East Pines and attacked Gene's Forest Rangers, but Gene helped the Park's employees to escape to the Cave in which there was a lava pit that can be used to dispose of the present. Once inside the Cave, Quillgin and his henchmen attacked the Park's employees in the ice bridge which led into the demise of Quillgin's henchmen after Benson broke the bridge with a pin ball.
However, Quillgin used a emergency stairs from the Cave to reach the Park's employees and threatened to kill them if they didn't give him the present. Quillgin almost succeeded in his goals before Mordecai decided to sacrifice himself by tackling Quillgin into the lava pit.
Rigby intervened in order to save his friend and jumped into the pit himself. When Rigby reached Mordecai and Quillgin, he fought Quillgin in the air and finally, he wished with the present a flying double skate board, that he and Mordecai used to fly out of the pit. Quillgin tried to reach his creation in his final moments for finally destroy the Christmas but ended up falling into the lava to his demise.